Early clinical and metabolic response to tazemetostat in advanced relapsed INI1 negative epithelioid sarcoma

Epithelioid sarcoma (ES) is a rare soft tissue sarcoma with an incidence of 0.05 per 100,000 population in the USA. It is characterized by multiple local recurrences and regional lymph nodes form the commonest site of metastases. The function of Integrase Inhibitor 1 (INI1) protein is lost in more than 90% of cases, which was the basis for the introduction of tazemetostat into the therapeutic armamentarium for management of advanced ES. The efficacy and manageable toxicity profile of tazemetostat have been demonstrated recently, leading to its accelerated approval for treatment of advanced ES. We report one of the first real-world cases of relapsed, metastatic ES treated with tazemetostat. The patient attained partial response with the therapy and is tolerating the drug well without serious toxicities. Lay abstract: Epithelioid sarcoma (ES) is a rare soft tissue sarcoma found in 0.05 people per 100,000 in the USA. It can recur multiple times in the lymph nodes of the involved site. ES involves the loss of the INI1 protein and this pathway is targeted by a new drug, tazemetostat. Recent studies have found this drug to be safe and effective for advanced ES. We have utilized this drug for a patient with metastatic ES who had history of multiple relapses. The patient had an encouraging response with the therapy and did not experience any serious side effects with this new drug.